Protective system for internal combustion engines



Jan. 14, 1969 M. c. RHOADS 3,421,489

PROTECTIVE SYSTEM FOR INTERNAL COMBUSTION ENGINES Filed March 1, 1967 United States Patent 5 Claims ABSTRACT OF THE DISCLOSURE A protective system for gasoline internal combustion engines using spark plugs. The engines are automatically stopped by short-circuiting the breaker contacts when either the engine is overheated or the oil pressure is too low. Circuitry is provided which permits emergency starting of the engine when the oil pressure is low.

Background of 'the invention This invention relates to a protective system for gasoline engines and operates to turn oti the motors whenever the engine is heated above a maximum temperature or when the oil pressure falls below a minimum value.

Modern gasoline engines are reasonably well adjusted for temperature variations and for constant oil pressure. Various compensating devices have been used to maintain the temperature of the engine and the pressure of the oil constant at all speeds and ambient conditions. However, when the oil is partially consumed or when the oil pump fails, the compensating devices cannot keep the oil pressure at a safe value and severe damage may result. In like manner, there are times when the engine coolant system is blocked and the temperature of the engine rises above a safe value. Continued operation under these conditions causes serious damage. The present invention stops the engine whenever these conditions are present before damage to the engine due to careless running.

Description of the drawing The single figure is a schematic diagram of connections showing the invention applied to a gasoline engine.

Description of preferred embodiment Referring to the figure, the protective system includes a temperature sensing means which is secured to some portion of the cooling system, such as a conduit 11 carrying a liquid coolant 12. Best results are obtained when the sensing means includes a screw 13 made of heat conductive material, such as copper or brass, threaded into a wall of the conduit 11 so that the end of the screw is in direct contact with the liquid coolant 12. Screw 13 is terminated by a fiat disk portion 14 on which a bimetallic strip 15 is positioned. The strip is secured at one end by a screw 16 while a contact disk 17 is welded to the other end. A cooperating contact disk 18 is mounted on a short strip 20 above the contact disk 17. A suitable block 21 holds the strip 20. A dust cover 22 may be mounted over the contacts to keep them clean. The bimetallic strip is mounted so that it will bend upwardly and force contacts 17 and 18 to close when the temperature of the liquid coolant 12 rises above the normal or safe temperature, generally 212 degrees Fahrenheit. The bimetallic strip 15 is grounded to the engine frame while the short strip 20 is connected to a conductor 23.

A pressure sensing device 24 is mounted on one of the conduits 25 which convey lubricating oil 26 from an oil pump (not shown) to the engine parts to be lubricated. A short conduit 27 is threaded into the oil conduit 25 and its upper end is terminated by a flat flange 28 across which 3,421,489 Patented Jan. 14, 1969 an elastic metal diaphragm 30 is mounted. The diaphragm is secured only at its edge so that it can be flexed or bowed upwardly by the pressure in conduit 25. An insulator knob 31 is mounted at the center of the diaphragm 30 and is designed to make contact with a flexible strip 32, secured to a support 33 at one end and carrying a contact disk 34 at its other end. When the oil is not under pres sure, the diaphragm 3G is fiat as shown in the figure and contact disk 34 rests on another contact disk 35, secured to a short strip 36 mounted in an insulator block 37. Contacts 34 and 35 remain closed until the pressure of the oil in conduit 25 forces the diaphragm up and separates the contacts. In the normal running position, contacts 34 and 35 remain open.

The contacts 17, 18 in the temperature sensing means 10 and the contacts 34, 35 in the pressure sensing means are connected to conductor 23 and to a pair of normally closed contacts 40 on a guard relay 41 which includes a winding 42. The guard relay 41 is operated only when the engine is started and during the starting operation contacts 40 are opened in order to disable the temperature and pressure sensing means.

The engine equipment as shown in the figure includes a direct current source of electrical power 43 (which may be a storage battery) and a start motor 44 which is coupled to the engine 45 by means of a mechanical coupling 46. The start motor is energized by means of a switch 47 which is depressed by an operator during the starting operation. The contacts under the start switch 47 are connected in series with a winding 48 of a start relay 50 having contacts 51. These engine components are well known in the art and since they do not form a part of the invention they need not be described here in detail. The engine also includes an ignition coil 52 connected in series with an ignition switch 53, the battery 43, and a pair of breaker contacts 54. The breaker contacts are operated by a cam 55 to open and close in synchronism with the operation of the pistons in the engine combustion chambers. The secondary winding of the ignition coil is connected to a distributor 56, also run by the engine, and a plurality of spark plugs 57, only one of which is shown in the figure. These components are also well known in the art and their details of construction and operation need not be described in detail.

The operation of this circuit is as follows: when the engine is at rest the coolant 12 is presumably at a low temperature and the bimetallic strip 15 is in the position shown in the figure, holding contacts 17 and 18 in their open position. The pressure of the oil 26 in conduit 25 is presumed to be considerably less than the operating pressure since the oil pump is not operating and for this reason disk 30 is flat as shown in the figure and contacts 34, 35 are closed. Under these conditions the engine cannot start because contacts 34, 35 are connected through closed contacts 40 and short-circuit the primary winding of the ignition coil, the ignition switch, and the batery 43. However, when start switch 47 is depressed and the start relay 50 connects contacts 51, the guard relay 41 is energized and contacts 40 are opened. Contacts 51 also complete a circuit to the start motor 44 and the engine is turned over for several revolutions during which time it should start. During this starting operation the oil pump (not shown) is operated and creates an oil pressure which opens contacts 34, 35 before the operator releases start switch 47. As soon as the start switch is opened, the start relay is normalized and the start motor 44 stops. At this time the guard relay 41 is normalized and contacts 40 are closed. This is the running position and with contacts 40 closed the temperature sensing means 10 and the pressure sensing means 24 are in operation to protect the engine from excess temperatures and from oil pressures that are to low. If the temperature of the engine rises above a predetermined temperature, about 212 degrees F., the bimetallic strip 15 will curve upwardly until contacts 17 and 18 are closed. This puts a shortcircuit across the ignition coil and the battery and the spark plugs 57 will not operate. The engine will stop and, while it may be turned over by the start motor, it cannot run without the start switch being depressed.

The pressure sensing means 24 operates in a similar manner. The oil 26 in conduit 25 presses against the resilient diaphragm 3t) and moves knob 31 upwardly to maintain contacts 34 and 35 in an open position. If the oil pressure is reduced for any reason at all, such as lack of oil or failure of the oil pump, the diaphragm will move to its original position, close contacts 34, 35 and again short-circuit the ignition coil 52 and stop the engine.

Having thus fully described the invention, what is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A protective system for internal combustion engines employing pistons in combustion chambers comprising:

(a) a temperature sensing means coupled to a conduit carrying a cooling liquid for the engine and including a pair of normally open electrical contacts which close when the temperature of the liquid rises above a predetermined value;

(b) a pressure sensing means coupled to the lubricating oil system of the engine and including a resilient diaphragm responsive to the pressure in the oil system and a pair of contacts operated by the the diaphragm which remain open as long as the oil pressure is above a predetermined value;

(c) fuel igniting means in the combustion chambers for igniting a fuel-air mixture in the chambers to keep the engine running;

(d) an electrical start motor mechanicaly coupled to the engine for starting it;

(e) a start relay including a winding connected in series with a source of electrical power and a start switch,

and a pair of contacts connected in series with the start motor and a source of electrical power;

(f) and a guard relay circuit for disabling the temperature sensing means and the pressure sensing means during a starting operation, said circuit including a relay winding connected in series with a contact on the start relay and ground, and a connection between the contacts of each sensing means and a pair of contacts on the guard relay for disabling the two sensing means whenever the engine is started.

2. A protective system as claimed in claim 1 wherein the pair of contacts in the temperature sensing means is coupled to a bimetallic strip which is distorted and closes the contacts when the temperature rises above a predetermined value to disable the ignition system.

3. A protective system as claimed in claim 1 wherein said pressure sensing means is connected to an oil conduit connected to the high pressure side of an oil pump.

4. A protective system as claimed in claim 1 wherein the electrical igniting means includes an ignition coil, breaker contacts, a distributor, and a spark plug in each combustion chamber.

5. A protective system as claimed in claim 1 wherein the contacts on the guard relay are connected in series with the contacts in the temperature and pressure sensing means and wherein the guard relay winding is connected in series between the contacts of the start relay and a source of electrical power.

References Cited UNITED STATES PATENTS 7/1930 E. Slinger 123-1465 8/1951 Newman et al 123-1465 

